Brakes of the sliding caliper disc brake type have been in use for many years. One of the most common types is disclosed in U.S. Pat. No. 3,628,639-Daley, Jr., issued Dec. 21, 1971. The type of caliper support mechanism shown in that patent has a fixed member provided with removable caliper mounting or support pins located to support the caliper housing at either end while the fixed member takes the brake torque reaction forces from the caliper housing. The support pins extend through ears or lugs formed on the caliper housing, commonly with two such ears or lugs at each end of that housing. The ears or lugs of each end are transversely bored in axial alignment so that the support pins fit into the transverse bores in sliding relation. It is common to provide rubber-like rings in internal grooves of the transverse bores to prevent metal-to-metal contact and unnecessary noise while permitting the caliper to slide transversely on the support pins as the brake is energized and deenergized.
As the brake shoes wear, these rubber-like rings slide on progressively moving limited areas on the outer surfaces of the support pins. While the rings are recessed in the transverse bores, they and the surfaces of the support pins within the bores are still subjected to damage from water, chemicals, dust and other debris from the roadway.